I am not a specialist, but your exclude zone is Far too wide and/or you need to add some basic autogen around the airport.
That's the problem. Since, as you said yourself, you are not a specialist, you are assuming the scenery as a "bug", that the bug is the exclusion zone, and it can be fixed relatively easily. Don't you think that, if it was an easy fix, we would have fixed it ourselves long time ago ?
The missing autogen is NOT caused by an exclusion zone!
The problem is caused by a side effect of a special FS9 command used in FSX, that is needed to create the custom ground, without having ground flickering issues. The amount of the effect is related to the size of the ground polygons tiles AND even to the airport heading compared to an hypotetical north oriented ground polygon grid. Nothing related to exclusion zones in any way.
An hypotetical fix would require redoing the ground polygonal grid in smaller steps. But that will NOT fix it entirely! It would simply reduce the size of the exclude autogen. But, it would have other side effects too because, assuming we are now losing autogen up to 4 km outside the airport (it's not a correct number, I'm just making an example), if we decrease the grid size in half, the problem will still appear, at 2 km, but the number of ground polygons would increase 4 times. If we would like to reduce the effect at 1 km, the number of polygons would increase 16 times! AND, it wouldn't be just that, on top of increasing the number of polygons, since each polygon is mapped to a texture, we'll increase also the number of materials used. Since each material change on the video card is costly, an important fps optimization step is to keep the number of material changes as low as possible so, it's better to draw less larger textures than to draw more smaller textures. So, this fix would increase BOTH the number of poygons AND the number of materials at least 4 times, and perhaps even 16 times, if we want to reduce the effect to be less noticeable. And, nonetheless, it will NOT go away entirely.
We always put performances first. Everybody is able to create a nice and slow scenery, but we try to create nice and fast sceneries so, there's no way we destroy our good performances only to gain some autogen, which will decrease fps even further...
Some other possible solutions would also have worse side effect than the disappearing autogen. For example, switching to a native FSX photoreal background, like in KORD or KJFK, would DECREASE the ground sharpness compared to the current version. People will rightly complain that the "fix" fixed the autogen, but made the whole scenery look worse.
This is what happens each time an FS9 command is used in FSX: unexpected side effects appears, like in the case of missing AI at Zurich, when used with FS9 AI models, because of the FS9 commands needed to create the custom runway texture (which of course is not possible to create in any other way).
But unfortunately, the definitive solution wouldn't make much commercial sense: because it would mean designing airports without custom ground in a fully FSX native mode (using only AFCAD ground), something that the market doesn't accept.
Also, it seems that the problem is more apparent with CH Pro. You might believe it or not but, according to our download stats, only 2% of Zurich users downloaded the specific CH Pro version. At THIS low rate of usage, we might not even be able to *buy* a copy of it to check for compatibility, let alone spending time to analyze the problem or looking into alternative solutions.
We can't be more satisfied of how Zurich sales are doing and this, added to the very low usage of the CH Pro version, gives us just one conclusion: the CH Pro autogen issue didn't matter to a lot of users. Unfortunately, scenery design is just a list of compromises, and there's no way we can have everybody happy, we can only try to accomodate what appears to be the majority.